Multi tool use

Create (and persist) file from Java in Docker container

I am developing a Java Spring Boot application meant to run in a Docker container. When I run the image, I need the app to check if a file exists in a path, and to create it if does not exist. When I stop the container and start it again, the file is missing again.
How can I achieve this? Do I need to mount a volume on the host?

-v

volumes:

docker-compose

docker container list

stopped

docker start

docker run

2 Answers
2

Let's say your Java app called app that saves a file in:

app

/var/lib/data


Then you should launch your container as follows:

docker volume create app-data

docker run -p 8080:8080 --mount source=app-data,target=/var/lib/data app


This will store all your data in a persistent volume named app-data

app-data

You can also bind a directory between the host machine and the container as follows:

docker run -p 8080:8080 --volume /var/lib/data:/var/lib/data app


This will store everything in /var/lib/data on the host rather than in the container. That way, the next time you start the container, it reads from there.

/var/lib/data

I typically go with the first option, as I have a name for the data I am storing, and it is not changing the "state" of the host machine (arguably still is, but very minimally). Binding a directory leaves room for error if any other process running on the host touches that directory.

See: https://docs.docker.com/storage/volumes/

Ok as @Ben suggested it is working fine when I stop/start the container instead of running it.

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